User guide contains following:
Usually, an extension is instantiated only once.
It's not very clear when extension can be instantiated many times? I'm supporting test suite with multiple extensions and every extension stores it's state in class fields. Everything works fine, but can I rely on this or should I refactor this code to use ExtensionContext.Store?
Usually, an extension is instantiated only once. So the question becomes relevant: How do you keep the state from one invocation of an extension to the next?
I think this sentence shall highlight that the same instance of an extension might be re-used for multiple tests. I doubt that the instance might be replaced in the middle of a test.
Multiple instances of an extension might be instantiated when a test uses programmatic extension registration (with @RegisterExtension). In such case, the test class creates its own instance of the extension. JUnit cannot reuse this instance in other test classes. But an instance created by declarative extension registration (with @ExtendWith) might be used for multiple test classes.
